Group III nitride compound semiconductor device

ABSTRACT

A group III nitride compound semiconductor device has a substrate, a group III nitride compound semiconductor layer having a device function, and an undercoat layer formed between the substrate and the group III nitride semiconductor layer. The undercoat layer has a surface which has a texture structure, or which is trapezoid shaped in section or which is pit shaped. In addition, a reflection layer made of nitride of at least one metal selected from the group consisting of titanium, zirconium, hafnium and tantalum may be formed on a surface of the undercoat layer. Also the surface of the reflection layer is formed as a texture structure, a trapezoid shape in section or a pit shape.

[0001] This is a Continuation-In-Part of application Ser. No.09/058,586, filed on Sep. 8, 2000, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a group III nitride compoundsemiconductor device.

[0004] The present application is based on Japanese Patent ApplicationsNo. Hei. 11-276556, 2000-41222, 2000-191779 which are incorporatedherein by reference.

[0005] 2. Description of the Related Art

[0006] A group III nitride compound semiconductor device is used in alight-emitting device such as a light-emitting diode, etc. Such alight-emitting device has a configuration in which a group III nitridecompound semiconductor layer having a device function is epitaxiallygrown on a surface of a substrate, for example, formed of sapphire.

[0007] The internal stress is, however, generated between the sapphiresubstrate and the group III nitride semiconductor layer because thesapphire substrate is different in thermal expansion coefficient andlattice constant from the group III nitride compound semiconductorlayer. As a phenomenon caused by the internal stress, a bowing occurs ina growth of the group III nitride compound semiconductor on the sapphiresubstrate. If the bowing becomes too large, the crystallinity ofsemiconductor not only may be spoiled, but that the semiconductor layermay also has many cracks. And inconvenience occurs in alignment ofphotolithography at the time of production of the device.

[0008] In the background art, therefore, a so-called low-temperaturebuffer layer was formed between the substrate and the group III nitridecompound semiconductor layer to thereby relax the internal stress.

[0009] The growth temperature of the group III nitride compoundsemiconductor layer for forming a device by a general metal organicchemical vapor deposition method (hereinafter referred to as “MOCVD”method) is 1000° C. or higher. On the other hand, the growth temperatureof the low-temperature internal stress layer is approximately in a rangeof from 400 to 500° C. Hence, the temperature history of from the stepof cleaning the substrate at about 1000° C. to the growth of the groupIII nitride compound semiconductor layer is high temperature (1000°C.)→low temperature (400 to 500° C.)→high temperature (1000° C.). Hence,not only was, it difficult to control the temperature but also thermalefficiency was poor.

[0010] It may be, therefore, conceived that the buffer layer is formedat a high temperature. The problem of bowing, however, occurs again if agroup III nitride compound semiconductor (for example, an AlN layer thesame as the low-temperature buffer layer) is grown directly on thesubstrate at a high temperature of about 1000° C.

SUMMARY OF THE INVENTION

[0011] The inventors of the present invention have made investigationover and over again to solve the problem of bowing. As a result, theinventors thought up the present invention as follows:

[0012] A group III nitride compound semiconductor device comprises anundercoat layer having a surface on which a group III nitride compoundsemiconductor layer having a device function can be formed, the surfaceof the undercoat layer containing inclined faces, wherein the projectedarea ratio of the inclined faces to the whole surface of the undercoatlayer on a plane of projection is in a range of from 5 to 100%.

[0013] According to another aspect, preferably, the undercoat layercontaining inclined faces is formed as a texture structure. Here, the“texture structure” means a structure in which the surface of theundercoat layer is shaped like teeth of a saw in any sectional vies,that is, a combination of a peak and a trough is repeated through aninclined face. The peaks may Include those which are independent of eachother as polygonal pyramids (inclusive of cones) or those which arestanding in a row like a mountain range.

[0014] In this specification, a “sectional trapezoid shape” means ashape in which there is a flat region at the top of each peak, and ashape in which the flat region is wider is referred to as a “pit shape”.

[0015] In this specification, when the projected area ratio occupied bythe inclined face region on a whole plane of projection is in a range offrom 70 to 100%, the shape is referred to as a “texture structure”; whenthe projected area ratio is in a range of from 30 to 70%, the shape isreferred to as a “sectional trapezoid shape”; and when the projectedarea ratio is in a range of from 5 to 30%, the shape is referred to as a“pit shape”.

[0016] Use of the aforementioned undercoat layer relaxes internal stressbetween the group III nitride compound semiconductor layer and thesubstrate including the undercoat layer. It is supposed that internalstress applied to a hetero interface is relaxed by acting in directionsparallel to the inclined faces because of the presence of the inclinedfaces in the hetero interface. If internal stress is relaxed in theaforementioned manner, the problem of bowing is reduced. As a result,not only can the group III nitride compound semiconductor layer beprevented from cracking, but also the crystallinity of the group IIInitride compound semiconductor layer can se improved. Moreover, itbecomes easy to perform alignment of photolithography at the time ofproduction of the device.

[0017] Hereupon, the undercoat layer transmits light having a wavelengthof not smaller than 360 nm because the undercoat layer is made of agroup III nitride compound semiconductor. Incidentally, when theundercoat layer is made of AlN (refractive index: 2.12) and the groupIII nitride compound semiconductor layer provided on the undercoat layeris made of GaN (refractive index: 2.60), the angle of incidence of lighton the undercoat layer must be selected to be not larger than about 22degrees so that light given from the GaN side is totally reflected onthe undercoat layer. In the case of an undercoat layer having theaforementioned texture structure, it is impossible to obtain totalreflection surely on the whole surface of the undercoat layer though itmay be said that the reflectivity of the undercoat layer is relativelyhigh because the angle of incidence of light on the surface of theundercoat layer becomes small.

[0018] From the above point of view, the present invention may beconfigured as follows.

[0019] A group III nitride compound semiconductor device comprises: asubstrate; a group III nitride compound semiconductor layer having afunction of light-emitting device or a function of a photodetectorlight-receiving device unction; an undercoat layer formed between thesubstrate and the group. III nitride compound semiconductor layer andmade of a group III nitride compound semiconductor, the undercoat layerhaving a surface formed as a texture structure or shaped like trapezoidsin section, or like pits; and a reflection layer formed on the surfaceof the undercoat layer and made of nitride of at least one kind of metalselected from the group consisting of titanium, zirconium, hafnium andtantalum, the reflection layer having a surface shape formed inaccordance with the surface shape of the undercoat layer.

[0020] According to the group III nitride compound semiconductor deviceconfigured as described above, a reflection layer made of predeterminedmetal nitride is formed on the surface of the undercoat layer having asurface shape such as a texture structure, a trapezoid shape in sectionor a pit shape. The reflection layer also has such a surface shape as atexture structure, a trapezoid shape in section or a pit shape becausethe reflection layer is formed in accordance with the surface shape ofthe undercoat layer.

[0021] The reflection layer made of metal nitride has a so-calledmetallic-color mirror surface. Moreover, the angle of incidence of lighton the surface of the texture structure, trapezoid shape in section orpit shape from the group III nitride compound semiconductor layer can bemade smaller. Hence, the reflection latter according to the presentinvention can substantially totally reflect light incident on thereflection later from the group III nitride compound semiconductor layerside.

[0022] The inventors of the present invention have already proposednitride of at least one metal selected from the group consisting oftitanium, zirconium, hafnium and tantalum so that a group III nitridecompound semiconductor can be grown with good crystallinity on the metalnitride when the metal nitride is used as the aforementionedpredetermined metal nitride (see Japanese Patent Publication No. Hei.2000-323753). Also in the case where a group III nitride compoundsemiconductor is to be grown on a reflection layer made of theaforementioned metal nitride, internal stress between the group IIInitride compound semiconductor layer and the substrate inclusive of thereflection layer and the undercoat layer can be relaxed because thesurface of the reflection layer is formed as a texture structure, atrapezoid shape in section or a pit shape. As similar to theaforementioned, it is conceived that stress applied on a heteroInterface is diffused in parallel to the inclined faces because of thepresence of the inclined faces in the hetero interface and, accordingly,the stress can be relaxed. When internal stress is relaxed in theaforementioned manner, the bowing problem or cracking is reduced.Moreover, the crystallinity of the group III nitride compoundsemiconductor layer is improved, and the group III nitride compoundsemiconductor layer can be aligned easily when the device is produced.

[0023] Features and advantages of the invention will be evident from thefollowing detailed description of the preferred embodiments described inconjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The file of this patent contains at least one drawing executed incolor. Copies of this patent with color drawings will be provided by thePatent and Trademark Office upon request and payment of the necessaryfee.

[0025]FIG. 1 is a sectional view showing an undercoat layer of a texturestructure;

[0026]FIG. 2 is a surface SEM photograph showing an undercoat layer of atexture structure;

[0027]FIG. 3 is a surface SEM photograph showing an undercoat layer of asectional trapezoid shape;

[0028]FIG. 4 is a surface SEM photograph showing an undercoat layer of apit shape;

[0029]FIG. 5 is a graph showing the quantity of bowing of a substrate;

[0030]FIG. 6 is a sectional view showing bowing of a substrate;

[0031]FIG. 7 shows a light-emitting diode according to an embodiment ofthe present invention;

[0032]FIG. 8 shows a light-emitting diode according to anotherembodiment of the present invention;

[0033]FIG. 9 is a surface SEM photograph of an undercoat layer accordingto the embodiment shown in FIG. 8;

[0034]FIG. 10 is a graph for comparison between the light outputintensity of the light-emitting diode as the embodiment shown in FIG. 8and the light output of a light-emitting diode as a comparative example;

[0035]FIG. 11 shows a light-emitting diode according to a still anotherembodiment of the present invention; and

[0036]FIG. 12 shows a light-emitting diode according to a still anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] Respective constituent parts of the present invention will bedescribed below in detail.

[0038] Substrate

[0039] The material of the substrate is not particularly limited so longas an undercoat layer made of a group III nitride compound semiconductorcan be formed on the substrate. Examples of the substrate material whichcan be used include: hexagonal-crystal such as sapphire, SiC (siliconcarbide), GaN (gallium nitride), etc.; and cubic-crystal such as Si(silicon), GaP (gallium phosphide), GasA (gallium arsenide), etc.

[0040] Group III Nitride Compound Semiconductor Layer

[0041] A group III nitride compound semiconductor is represented by thegeneral formula Al_(X)Ga_(Y)In_(1-X-Y)N (0≦X≦1, 0≦Y≦1, 0≦X+Y≦1), whichincludes so-called binary compounds such as AlN, GaN and InN, so-calledternary compounds such as Al_(x)Ga_(1-X)N, Al_(X)In_(1-X)N andGa_(X)In_(1-X)N (0≦X≦1 in the above), and so-called quaternary compoundssuch as Al_(X)Ga_(Y)In_(1-X-Y)N (0≦X≦1, 0≦Y≦1, 0≦X+Y≦1). The group IIIelements may be partially replaced by boron (B), thallium (Ti), etc. Thenitrogen (N) may be partially replaced by phosphorus (P), arsenic (As),antimony (Sb), bismuth (Bi), etc.

[0042] The group III nitride compound semiconductor may contain anyoptional dopant. Si, Ge, Se, Te, C, etc. may be used as n-typeimpurities. Mg, Zn, Be, Ca, Sr, Ba, etc. may be used as p-typeimpurities. Incidentally, after doped with p-type impurities to reducethe resistance, the group III nitride compound semiconductor may besubjected to electron beam irradiation, plasma irradiation or heating bymeans of a furnace.

[0043] The group III nitride compound semiconductor maybe formed by ametal organic chemical vapor deposition method (MOCVD method) or anyother known method such as a molecular beam epitaxy method (MBE method),a halide vapor phase epitaxy method (HVPE method), a sputtering method,an ion-plating method, or the like.

[0044] Examples of the device formed from the group III nitride compoundsemiconductor include optical devices such as a light-emitting diode, aphotodetector, a laser diode, a solar cell, etc.; bipolar devices suchas a rectifier, a thyristor, a transistor, etc.; unipolar devices suchas an FET, etc.; and electronic devices such as a microwave device, etc.

[0045] Incidentally, a homo structure, a single hetero structure or adouble hetero structure with an MIS junction, a PIN junction or a p-njunction may be used as the configuration of the light-emitting deviceor the photodetector. A quantum well structure (a single or multiplequantum well structure) may be used as the light-emitting layer and/orthe clad.

[0046] The undercoat layer is not specifically limited if theaforementioned group III nitride compound semiconductor can be grown onthe undercoat layer.

[0047] In an embodiment, the undercoat layer is constituted by a firstgroup III nitride compound semiconductor layer formed on a substrate.

[0048] Examples of the first group III nitride compound semiconductorformed on the substrate include quaternary compound semiconductorsrepresented by Al_(X)Ga_(Y)In_(1-X-Y)N (0≦X≦1, 0≦Y≦1, 0≦X+Y≦1), ternarycompound semiconductors represented by Al_(X)Ga_(1-X)N (0≦X≦1), andbinary compound semiconductors by AlN, GaN and InN. Especially, AlN ispreferably used on a sapphire substrate.

[0049] Each of these first group III nitride compound semiconductorlayers substantially has a single crystal structure.

[0050] The inclined faces are formed in the surface of the undercoatlayer. A base structure forming the inclined faces may include polygonalpyramids such as triangular pyramids, quadrilateral pyramids, etc., orstructures like a mountain range in which peaks and troughs areconnected alternately by belt-like inclined faces. The inclined facesare formed on the whole surface of the undercoat layer. Each of theinclined faces is so small as to have a width smaller than 2 μm on aplane of projection. The projected area ratio of the inclined faces tothe surface of the undercoat layer on a plane of projection is set to bepreferably in a range of from 5 to 100%, more preferably in a range offrom 30 to 100%, further preferably in a range of from 70 to 100%.

[0051] If the projected area ratio of the inclined faces on a wholeplane of projection is in a range of from 70 to 100%, the surface of theundercoat layer exhibits a texture structure as shown in FIGS. 1 and 2and is shaped like mountains in section. If the projected area ratio is100%, the surface of the undercoat layer exhibits a structure in which acombination of a peak and a trough is repeated like teeth of a saw.

[0052] If the projected area ratio of the inclined faces on a wholeplane of projection is in a range of from 30 to 70%, the surface of theundercoat layer is shaped like trapezoids in section so that insularportions and mountain portions coexist as shown in FIG. 3.

[0053] If the projected are ratio or the inclined faces on a plane ofprojection is in a range of from 5 to 30%, the surface of the undercoatlayer is shaped like pits so that holes are formed in a flat surface asshown in FIG. 4.

[0054] Here, the “plane of projection” means a plane of projectionobtained by performing parallel projection of the surface of theundercoat layer onto a plane parallel with the substrate.

[0055] The first group III nitride compound semiconductor layer having arough surface as described above is formed by pouring a larger amount ofammonia gas (NH₃) than the general growth condition and at a hightemperature (about 1,150° C.) which is substantially the sametemperature as a second group III nitride compound semiconductor havinga device function will be formed.

[0056] Next, an experimentation for confirming the effect of the presentinvention will be described below.

[0057] An AlN layer was formed on a sapphire substrate by the MOCVDmethod for a reference sample. A 4 μm thick GaN layer was further formedon the AlN layer by the MOCVD method. The quantity of bowing of eachsample at room temperature was as shown in FIG. 5. As shown in FIG. 6,the quantity of bowing was measured as the center height H of eachsample. In FIG. 5, the symbol  indicates a result in the case where thegrowth temperature and thickness of the AlN layer were 400° C. and 200 Årespectively. The symbol ▾ indicates a result in the case where thegrowth temperature and thickness of the AlN layer as a layer having aflat surface were 1,130° C. and 1.5 μm respectively. It was apparentfrom FIG. 5 that a large quantity of bowing occurred in the laminatewhen the AlN layer had a flat surface.

[0058] On the other hand, the reference symbol ◯ shows the embodiment ofthe present invention. In this case, the AlN layer had a surface of atexture structure as shown in FIGS. 1 and 2 and the growth temperatureand thickness of the AlN layer were. 1,130° C. and 1.5 μm respectively.It was apparent from the result of FIG. 5 that a small quantity ofbowing equivalent to that of the background-art low-temperature bufferlayer () is shown when the AlN layer had such a texture structure.Moreover, variation in bowing became small.

[0059] Moreover, the full width at half-maximum (FWHM) of a rockingcurve of the GaN layer formed on the AlN layer having such a surfacetexture structure was 16 seconds. This value was approximately equal tothat of an n-type GaN contact layer used in an existing light-emittingdevice. Hence, this value exhibited sufficient crystallinity to serve asa group III nitride compound semiconductor layer having a devicefunction.

[0060] Alternatively, after an undercoat layer having a flat surface isgrown, the flat surface may be treated by a method such as etching,etc., to thereby shape the surface of the undercoat layer into a texturestructure, or like a sectional trapezoid shape or like a pit shape.

[0061] Preferably, a sedimentary layer may be formed between thesubstrate and the undercoat layer.

[0062] When the undercoat layer is formed of a group III nitridecompound semiconductor, the sedimentary layer may be preferably formedalso of a group III nitride compound semiconductor or of a metal nitridecompound semiconductor. Among the group III nitride compoundsemiconductors, preferably Al_(X)Ga_(1-X)N (0≦X≦1), more preferably AlNmay be used as the sedimentary layer. Among the metal nitride compoundsemiconductors, preferably one kind or a combination of two or morekinds selected from the group of titanium nitride, hafnium nitride,zirconium nitride and tantalum nitride, more preferably titanium nitridemay be used as the sedimentary layer. In this case, the substrate ispreferably formed of sapphire. More preferably, the sedimentary layer isformed on face a of the sapphire substrate.

[0063] A known method (such as an MOCVD method, a sputtering method, orthe like) for forming a group III nitride compound semiconductor or ametal nitride compound semiconductor can be used as a method for formingthe aforementioned sedimentary layer.

[0064] The thickness of the sedimentary layer is not particularlylimited but is set to be in a range of from several nm to hundreds nm(from tens Å to thousands Å).

[0065] According to the inventors' investigation, the interposition ofthe sedimentary layer between the substrate and the undercoat layer(distortion relaxing layer) makes the inclination in the surface of theundercoat layer easy to control That is, the condition for forming asurface Of a desired structure (such as a texture structure, a sectionaltrapezoid shape or a pit structure) is widened so that the surface ofthe desired structure is formed easily. Hence, a device having such anundercoat layer can be produced with good yield.

[0066] The sedimentary layer can be provided as a laminate of two ormore layers as follows.

[0067] An intermediate layer of a group III nitride compoundsemiconductor, preferably AlN or GaN, is formed on a first sedimentarylayer which is formed on the substrate. A second sedimentary layer isformed on the intermediate layer (this operation may be repeated). Theundercoat layer is formed on the second sedimentary layer.

[0068] The composition of the first sedimentary layer may be the same asor different from that of the second sedimentary layer.

[0069] Also the thickness of the intermediate layer is not particularlylimited.

[0070] Reference is made to Japanese Patent Publications No.Hei.7-267796 and 9-199759 as examples in which a plurality ofsedimentary layers are formed.

[0071] Further, reflection layer made of nitride may be formed on thesurface of the undercoat layer.

[0072] As the material for forming the reflection layer, at least onemember may be selected from the group consisting of titanium nitride,hafnium nitride, zirconium nitride and tantalum nitride. Especially,titanium nitride is preferably used. The method for growing the metalnitride is not particularly limited but examples of the available methodinclude: CVD (Chemical Vapor Deposition) such as plasma CVD, thermalCVD, optical CVD, or the like; PVD (Physical Vapor Deposition) such assputtering, reactive sputtering, laser ablation, ion plating,evaporation, or the like; and so on.

[0073] The thickness of the reflection layer is preferably selected tobe in a range of from 0.1 to 5.0 μm. If the thickness of the reflectionlayer is larger than the upper limit, there is a risk that the roughnessof the surface of the undercoat layer is lost so that the surface of thereflection layer is flattened. As a result, it becomes impossible toexpect relaxation of stress on the hetero interface between thereflection surface and the group III nitride compound semiconductorlayer. If the thickness is smaller than the lower limit, reflection oflight becomes insufficient. Especially, the thickness of the reflectionlayer is preferably selected to be in a range of from 0.1 to 1.0 μm.More especially, the thickness of the reflection layer is preferablyselected to be in a range of from 0.2 to 0.5 μm.

[0074] The embodiment has been described above on the assumption that agroup III nitride compound semiconductor layer is grown on an undercoatlayer and a reflection layer having inclined faces so that the group IIInitride compound semiconductor layer serves directly as a devicefunction layer. Incidentally, the group III nitride compoundsemiconductor layer may be used as an intermediate layer so that asecond undercoat layer having inclined faces for relaxing distortion canbe formed on the intermediate layer (this operation may be furtherrepeated) Hence, the internal stress of the group III nitride compoundsemiconductor layer having a device function is further relaxed tothereby improve the crystallinity thereof.

[0075] The intermediate layer may have a surface containing inclinedfaces (of a texture structure, or the like) reflecting the surfacestructure of the undercoat layer or may have a flat surface.

[0076] The reflection layer is formed on the undercoat layer located inthe uppermost position.

[0077] Embodiments of the present invention will be described below.

[0078]FIG. 7 shows the configuration of a light-emitting diode 10according to an embodiment of the present invention.

[0079] Specifications of respective layers are as follows. LayerComposition Dopant (Thickness) Transparent electrode 19 p-type layer 18p-GaN Mg  (0.3 μm) Layer 17 Quantum well layer In_(0.15)Ga_(0.85)N  (35Å) Barrier layer GaN  (35 Å) The number of repetition of quantum welland barrier layers: 1 to 10 n-type layer 16 n-GaN Si  (4 μm) Undercoatlayer 15 AlN  (1.5 μm) Substrate 11 Sapphire (350 μm) (face a)

[0080] The n-type layer 16 may be made to have a double-layeredstructure with an n⁻ layer of low electron density on the light-emittinglayer 17 side and an n⁺ layer of high electron density on the undercoatlayer 15 side.

[0081] The layer 17 is not limited to the superlattice structure. Asingle hetero structure, a double hetero structure, a homo-junctionstructure, or the like, may be used as the configuration of thelight-emitting device.

[0082] A group III nitride compound semiconductor layer which is dopedwith an acceptor such as magnesium and which has a wide band gap may beinterposed between the layer 17 and the p-type layer 18. This is aimedat prevention of electrons imported into the light-emitting layer 17,from diffusing into the p-type layer 18.

[0083] The p-type layer 18 may be made to have a double-layeredstructure with a p⁻ layer of low hole density on the light-emittinglayer 17 side and a p⁺ layer of high hole density on the electrode side.Each of the quantum well layers may be formed of InGaAlN, including InN,GaN, InGaN and InAlN. Each of the barrier layers may be formed ofInGaAlN, including GaN, InGaN, InAlN and AlGaN, having a wider energygap than that of the quantum well layer.

[0084] The light-emitting diode having such a configuration as describedabove is produced as follows.

[0085] First, while a hydrogen gas (H₂) is circulated into a reactor ofan MOCVD apparatus, the sapphire substrate is heated to 1,130° C. tothereby clean the surface thereof.

[0086] Then, trimethylaluminum (TMA) and NH₃ are imported into thereactor at the same substrate temperature so that an undercoat layer 15of AlN is grown by an MOCVD method. When the AlN undercoat layer 15 isgrown to a predetermined thickness while TMA and NH₃ are imported in thecondition of 30 μmol/min and 3 SLM respectively on this occasion, thesurface of the AlN undercoat layer 15 has a texture structure as shownin FIGS. 1 and 2.

[0087] Similarly, if the flow rate of NH₃ in the aforementionedcondition is reduced to a value in a range of from ½ times to ⅓ times,the surface of the undercoat layer 15 has a sectional trapezoidstructure as shown in FIG. 3.

[0088] Similarly, if the flow rate of NH, in the aforementionedcondition is reduced to a value in a range of from ¼ times a {fraction(1/9)} times, the surface of the undercoat layer 15 has a pit structureas shown in FIG. 4.

[0089] In the condition for forming a flat AlN film on the sapphiresubstrate, if the growth rate of AlN in a direction of a c axis (thatis, in a direction perpendicular to the substrate) is compared with thegrowth rate of AlN in a direction perpendicular to the c axis (that is,in a direction parallel to the substrate) especially in an initial stageof formation of the AlN film, the latter speed is sufficiently larger.Hence, AlN is two-dimensionally grown in the direction parallel to thesubstrate and then three-dimensionally grown in the directionperpendicular to the substrate. That is, there is a time long enough toform a uniform growth site by migration of Al atoms and N atoms into thesurface of growth.

[0090] If the amount of N atoms on the growth surface is increasedagainst this condition, the growth rate of AlN in the directionperpendicular to the substrate becomes higher because Al atoms areparticularly bonded to N atoms in the surface of growth beforeappropriate migration of the Al atoms. As a result, growth in thedirection parallel to the substrate becomes so ununiform that a texturestructure can be produced. It may be safely said that an intermediatecourse of formation of the texture structure is a sectional trapezoidstructure or a pit structure.

[0091] Incidentally, if the amount of N atoms is increased more greatly,AlN is grown not as a single crystal but as grains.

[0092] Then, while the substrate temperature is kept, an n-type layer 16is formed and second group III nitride compound semiconductor layers 17and 18 after the n-type layer 16 are formed by an ordinary method (MOCVDmethod). In the growth method, an NH₃ and group III element alkylcompound gases such as trimethylgallium (TMG), trimethylaluminum (TMA)and trimethylindium (TMI) are supplied onto a substrate heated to asuitable temperature and are subjected to a thermal decompositionreaction to thereby make a desired crystal grow on the substrate.

[0093] Then, the p-type layer 18, the layer 17 and the n-type layer 16are partially removed by reactive ion etching with Ti/Ni as a mask.Thus, a portion of the n-type layer 16 on which an n-type electrode pad21 will be formed is exposed photo resist is Implied onto thesemiconductor surface uniformly. The photo resist of theelectrode-forming portion on the p-type layer 18 is removed byphotolithography. Thus, the p-type layer 18 of this portion is exposed.An Au—Co transparent electrode layer 19 is formed on the exposed portionof the p-type layer 18.

[0094] Then, a p-type electrode pad 20 and an n-type electrode pad 21are formed by vapor deposition in the same manner as described above.

[0095]FIG. 8 shows a light-emitting diode 30 according to anotherembodiment of the present invention. Same parts in FIGS. 7 and 8 arereferenced correspondingly. The description thereof will be thereforeomitted.

[0096] In the light-emitting diode 30 according to this embodiment, asedimentary layer 31 of AlN is interposed between the sapphire substrate11 and the undercoat layer 35.

[0097] Specifications of respective layers are as follows. LayerComposition Dopant (Thickness) Transparent electrode 19 p-type layer 18p-GaN Mg  (0.3 μm) Layer 17 Quantum well layer In_(0.15)Ga_(0.85)N  (3.5nm) Barrier layer GaN  (3.5 nm) The number of repetition of quantum welland barrier layers: 1 to 10 n-type layer 16 n-GaN Si  (4 μm) Undercoatlayer 35 AlN  (0.2 μm) Sedimentary layer 31 AlN  (15 μm) Substrate 11Sapphire (350 μm) (face a)

[0098] The light-emitting diode 30 having the above configuration isproduced as follows.

[0099] First, reactive sputtering of an aluminum target is performed ona sapphire substrate at a temperature of from 300 to 500° C. by an argonads sputtering apparatus while a nitrogen gas is imported. The sapphiresubstrate having AlN deposited thereon in the aforementioned manner isset into an MOCVD apparatus. While H₃ and NH₃ are imported, thesubstrate is heated to 1,130° C.

[0100] Then, TMA and NH₃ are imported in the condition of 30 μmol/minand 3 SLM respectively to thereby form an AlN undercoat layer 35. Thesurface of the undercoat layer 35 has a texture structure as shown inFIG. 9 which is a SEM photograph thereof.

[0101] The same method as shown in FIG. 7 is used as a method forforming an n-type layer 16 and layers after the n-type layer 16.

[0102] The light output of the light-emitting diode 30 formed accordingto this embodiment, and the light output of a light-emitting diode(known configuration) according to a comparative example in which thedistortion-relaxing undercoat layer 35 is omitted from the formerconfiguration are measured by a photo detector and compared with eachother (FIG. 10). In FIG. 10, the reference symbol ◯ shows the lightoutput of the light-emitting diode 30 according to the embodiment, andthe reference symbol  shows the light output of the light-emittingdiode according to the comparative example. It is apparent from FIG. 10that the light-emitting diode 30 of the embodiment achieves a higherlight output than that of the comparative example. It is supposed thatdistortion in the n-type layer 16, the light-emitting layer 17 and thep-type layer 18 which constitute a device structure is relaxed due tothe presence of the undercoat layer 35 to result in improvement ofcrystallinity of each layer.

[0103]FIG. 11 shows a light-emitting diode 50 according to a stillanother embodiment of the present invention. Same parts in FIG. 7 arereferenced correspondingly. The description thereof will be thereforeomitted.

[0104] In the light-emitting diode 50 according to this embodiment, areflection layer 25 of TiN with a thickness of 0.3 μm is interposedbetween the undercoat layer 15 and the n-type layer 16. Otherspecifications are same as those of the embodiment in FIG. 7.

[0105] In order to produce this light-emitting diode, after theformation of the undercoat layer 15, the sample is transferred to areactor of a DC magnetron sputtering apparatus. A DC magnetronsputtering method is carried out to form a reflection layer 25 of TiN.Then, the sample is transferred to an MOCVD apparatus. While thesubstrate temperature is kept at 1130° C., an n-type layer 16 is formed.Other steps are same as a method for producing the embodiment in FIG. 7.

[0106]FIG. 12 shows a light-emitting diode 70 according to a stillanother embodiment of the present invention. Same parts in FIG. 8 arereferenced correspondingly. The description thereof will be thereforeomitted.

[0107] In the light-emitting diode 70 according to this embodiment, areflection layer 25 of TiN with a thickness of 0.3 μm is interposedbetween the undercoat layer 35 and the n-type layer 16. Otherspecifications are same as those of the embodiment in FIG. 8. Itsproducing method is same as that of the aforementioned embodiments.

[0108] Although this specification has been described while alight-emitting device is taken as an example, the present invention maybe applied, of course, to various kinds of semiconductor devices and tolaminates as intermediates of these devices.

[0109] The present invention is not limited to the description or themode for carrying out the present invention and the description of theembodiment. It also includes various modifications that can be conceivedeasily by those skilled in the art, without departing from the scope ofclaim.

[0110] The following matters will be disclosed.

[0111] (21) A group III nitride compound semiconductor devicecomprising:

[0112] a substrate;

[0113] a group III nitride compound semiconductor layer having a devicefunction; and

[0114] an undercoat layer formed between the substrate and the group IIInitride semiconductor layer, the undercoat layer being mountain shapedin a section.

[0115] (22) a grout III nitride compound semiconductor devicecomprising:

[0116] a substrate;

[0117] a group III nitride compound semiconductor layer having a devicefunction; and

[0118] an undercoat layer formed between the substrate and the group IIInitride semiconductor layer, the undercoat layer having a surface withconcave and convex portions, wherein a projected area ratio of theconcave portions to the surface of the undercoat layer on a plane ofprojection is in a range of from 5 to 100%.

[0119] (23) A group III nitride compound semiconductor device accordingto the above paragraph (22), wherein the projected area ratio of theconcave portions to the surface of the undercoat layer on a plane ofprotection is in a range of from 30 to 100%.

[0120] (24) A group III nitride compound semiconductor device accordingof the above paragraph (22), wherein the projected area ratio of theinclined faces to the surface of the undercoat layer on a plane ofprotection is in a range of from 70 to 100%.

[0121] (25) A group III nitride compound semiconductor device accordingto any one of the above paragraphs (21) through (24), wherein theundercoat layer is formed substantially of a single crystal.

[0122] (26) A group III nitride compound semiconductor device accordingto the above paragraph (25), wherein the undercoat layer is formed of agroup III nitride compound semiconductor and formed on a sapphiresubstrate.

[0123] (27) A group III nitride compound semiconductor device accordingto the above paragraph (26), wherein the undercoat layer is formed of anAlN layer.

[0124] (28) group III nitride compound semiconductor device according tothe above paragraph (27), wherein the AlN layer has a thickness of from0.2 to 3.0 μm.

[0125] (29) A group III nitride compound semiconductor device accordingto the above paragraph (27), wherein the AlN layer has a thickness offrom 0.5 to 1.5 μm.

[0126] (29-1) A group III nitride compound semiconductor deviceaccording to any one of the above paragraphs (21) through (29), furthercomprising a sedimentary layer interposed between the undercoat layerand the substrate.

[0127] (30) A group III nitride compound semiconductor device accordingto any one of the above paragraphs (21) through (26), wherein theundercoat layer is formed of a silicon single crystal.

[0128] (41) A laminate comprising:

[0129] a substrate;

[0130] a group III nitride compound semiconductor layer having a devicefunction; and

[0131] an undercoat layer formed between the substrate and the group IIInitride semiconductor layer, the undercoat layer having a surface of atexture structure.

[0132] (42) A laminate comprising:

[0133] a substrate;

[0134] a group III nitride compound semiconductor layer having a devicefunction; and

[0135] an undercoat layer formed between the substrate and the group IIInitride semiconductor layer, the undercoat layer having a surface whichis trapezoid shaped in section.

[0136] (43) A laminate comprising:

[0137] a substrate;

[0138] a group III nitride compound semiconductor layer having a devicefunction; and

[0139] an undercoat layer formed between the substrate and the group IIInitride semiconductor layer, the undercoat layer having a surface whichis pit shaped.

[0140] (44) A laminate comprising:

[0141] a substrate;

[0142] a group III nitride compound semiconductor layer having a devicefunction; and

[0143] an undercoat layer formed between the substrate and the group IIInitride semiconductor layer, the undercoat layer having a surfacecontaining inclined faces, wherein a projected area ratio of theinclined faces to the surface of the undercoat layer on a plane ofprojection is in a range of from 5 to 100%.

[0144] (45) A laminate according to the above paragraph (44), whereinthe projected area ratio of the inclined faces to the surface of theundercoat layer on a plane of protection is in a range of from 30 to n100%.

[0145] (46) A laminate according to the above paragraph (44), whereinthe projected area ratio of the inclined faces to the surface of theundercoat layer on a plane of protection is in a range of from 70 to100%.

[0146] (47) A laminate according to any one of the above paragraphs (41)through (46), wherein the undercoat layer is formed substantially of asingle crystal.

[0147] (48) A laminate according to the above paragraph (47), whereinthe undercoat layer is formed of a group III nitride compoundsemiconductor and formed on a sapphire substrate.

[0148] (49) A laminate according to the above paragraph (48), whereinthe undercoat layer is formed of an AlN layer.

[0149] (50) A laminate according to the above paragraph (49) wherein theAlN layer has a thickness of from 0.2 to 3.0 μm.

[0150] (51) A laminate according to the above paragraph (49), whereinthe AlN layer has a thickness of from 0.5 to 1.5 μm.

[0151] (51-1) A laminate according to any one of the above paragraphs(41) through (51), further comprising a sedimentary layer interposedbetween the undercoat layer and the substrate.

[0152] (52) A laminate according to any one of the above paragraphs (41)through (46), wherein the undercoat layer is formed of a silicon singlecrystal.

[0153] (61) A laminate comprising:

[0154] a substrate;

[0155] a group III nitride compound semiconductor layer having a devicefunction; and

[0156] an undercoat layer formed between the substrate and the groupsIII nitride semiconductor layer, the undercoat layer being mountainshaped in section.

[0157] (62) A laminate comprising:

[0158] a substrate;

[0159] a group III nitride compound semiconductor layer having a devicefunction; and

[0160] an undercoat layer formed between the substrate and the group IIInitride semiconductor layer, the undercoat layer having a surface withconcave and convex portions, wherein a projected area ratio of theconcave portions to the surface of the undercoat layer on a plane ofprojection is in a range of from 5 to 100%.

[0161] (63) A laminate according to the above paragraph (62), whereinthe projected area ratio of the concave portions to the surface of theundercoat layer on a plane of protection is in a range of from 30 to100%.

[0162] (64) A laminate according to the above paragraph (62), whereinthe projected area ratio of the inclined faces to the surface of theundercoat layer on a plane of protection is in a range of from 70 to100%.

[0163] (65) A laminate according to any one of the above paragraphs (61)through (64), wherein the undercoat layer is formed n c substantially ofa single crystal.

[0164] (66) A laminate according to the above paragraph (65), whereinthe undercoat layer is formed of a group III nitride compoundsemiconductor and formed on a sapphire substrate.

[0165] (67) A laminate according to the above paragraph (66), whereinthe undercoat layer is formed of an AlN layer.

[0166] (68) A laminate according to the above paragraph (67), whereinthe AlN layer has a thickness of from 0.2 to 3.0 μm.

[0167] (69) A laminate according to the above paragraph (67), whereinthe AlN layer has a thickness of from 0.5 to 1.5 μm.

[0168] (69-1) A laminate according to any one of the above paragraphs(61) through (69), further comprising a sedimentary layer interposedbetween the undercoat layer and the substrate.

[0169] (70) A laminate according to any one of the above paragraphs (61)through (66), wherein the undercoat layer is formed of a silicon singlecrystal.

[0170] (84) A laminate comprising:

[0171] a substrate;

[0172] a group III nitride compound semiconductor layer having a devicefunction;

[0173] an undercoat layer formed between the substrate and the group IIInitride semiconductor layer; and

[0174] a sedimentary layer formed between the undercoat layer andsubstrate, the undercoat layer being formed of a group III nitridecompound semiconductor or a metal nitride compound semiconductor, theundercoat layer having a surface of a texture structure, a surface of asectional trapezoid shape, or a surface of a pit shape, the sedimentarylayer being formed of a group III nitride compound semiconductor.

[0175] (85) A laminate according to the above paragraph (84), whereinthe sedimentary layer is formed as a multilayer containing at leastfirst and second sedimentary layers and another group III nitridecompound semiconductor layer is interposed between the first and secondsedimentary layers.

[0176] (86) A laminate according to the above paragraph (84) or (85),wherein the sedimentary layer is formed of Al_(X)Ga_(1-X)N (0≦X≦1) andformed at a temperature lower than or equal to that of the undercoatlayer.

[0177] (87) A laminate according to the above paragraph (84) or (85),wherein the sedimentary layer is formed of a metal nitride compoundsemiconductor and formed at a temperature lower than or equal to that ofthe undercoat layer.

[0178] (88) A laminate according to the above paragraph (86), whereinthe sedimentary layer is formed of an AlN layer.

[0179] (89) A laminate according to any one of the above paragraphs (84)through (88), wherein the substrate is formed of sapphire.

[0180] (90) A laminate according to the above paragraph (89), whereinthe sedimentary layer is formed on face a of the sapphire substrate.

[0181] (100) A laminate comprising:

[0182] a substrate;

[0183] an undercoat layer formed on the substrate and made of a groupIII nitride compound semiconductor, the undercoat layer having a surfaceformed as a texture structure or shaped like trapezoids in section, orlike pits;

[0184] a reflection layer formed on the surface of the undercoat layerand made of nitride of at least one kind of metal selected from thegroup consisting of titanium, zirconium, hafnium and tantalum, thereflection layer having a surface shape formed in accordance with thesurface shape of the undercoat layer; and

[0185] a group III nitride compound semiconductor layer formed on thereflection layer.

[0186] (101) A laminate according to the paragraph (100), wherein thereflection layer is made of titanium nitride.

[0187] (102) A laminate according to the paragraph (100) or (101),wherein the undercoat layer is made of Al_(X)Ga_(1-X)N (0≦X≦1).

[0188] (103) A laminate according to the paragraph (102), wherein theundercoat layer is made of AlN.

[0189] (104) A laminate according to the paragraph (100) or (101),wherein the undercoat layer is made of InGaAlN.

[0190] (105) A laminate according to the paragraph (100) or (101),wherein the undercoat layer is made of InAlN or InGaN.

[0191] (106) A laminate according to any one of the paragraphs (100)through (105), wherein the substrate is made of sapphire or siliconsingle crystal.

[0192] (107) A laminate according to any one of the paragraph (100)through (106), further comprising a sedimentary layer interposed betweenthe undercoat layer and the substrate.

[0193] (108) A laminate according to the paragraph (100), wherein: thesubstrate is made of sapphire; the undercoat layer is made of AlN andhaving a surface formed as a texture structure; and the reflection layeris made of titanium nitride.

What is claimed is:
 1. A group III nitride compound semiconductor devicecomprising: a substrate; a group III nitride compound semiconductorlayer having a device function; and an undercoat layer formed betweensaid substrate and said group III nitride semiconductor layer, saidundercoat layer having a surface of a texture structure.
 2. A group IIInitride compound semiconductor device according to claim 1, wherein saidundercoat layer is formed substantially of a single crystal.
 3. A groupIII nitride compound semiconductor device according to claim 2, whereinsaid undercoat layer is formed of a group III nitride compoundsemiconductor and formed on a sapphire substrate.
 4. A group III nitridecompound semiconductor device according to claim 1, wherein saidundercoat layer is made of Al_(X)Ga_(1-X)N (0≦X≦1).
 5. A group IIInitride compound semiconductor device according to claim 4, wherein saidundercoat layer is formed of an AlN layer.
 6. A group III nitridecompound semiconductor device according to claim 5, wherein said AlNlayer has a thickness of from 0.2 to 3.0 μm.
 7. A group III nitridecompound semiconductor device according to claim 5, wherein said AlNlayer has a thickness of from 0.5 to 1.5 μm.
 8. A group III nitridecompound semiconductor device according to claim 1, wherein saidundercoat layer is formed of a silicon single crystal.
 9. A group IIInitride compound semiconductor device according to claim 1, furthercomprising a sedimentary layer interposed between said undercoat layerand said substrate.
 10. A group III nitride compound semiconductordevice according to claim 1, wherein said substrate is made of one ofsapphire, silicon single crystal and silicon carbide single crystal. 11.A group III nitride compound semiconductor device according to claim 1,further comprising a reflection layer formed on said surface of saidundercoat layer and made of nitride of at least one kind of metalselected from the group consisting of titanium, zirconium, hafnium andtantalum, said reflection layer having a surface shape formed inaccordance with a surface shape of said undercoat layer.
 12. A group IIInitride compound semiconductor device according to claim 11, whereinsaid reflection layer is made of titanium nitride.
 13. A group IIInitride compound semiconductor device according to claim 11, whereinsaid substrate is made of sapphire, said undercoat layer is made of AlNand having a surface formed as a texture structure, and said reflectionlayer is made of titanium nitride.
 14. A group III nitride compoundsemiconductor device comprising: a substrate; a group III nitridecompound semiconductor layer having a device function; and an undercoatlayer formed between said substrate and said group III nitridesemiconductor layer, said undercoat layer having a surface which istrapezoid shaped in section.
 15. A group III nitride compoundsemiconductor device according to claim 14, wherein said undercoat layeris formed substantially of a single crystal.
 16. A group III nitridecompound semiconductor device according to claim 15, wherein saidundercoat layer is formed of a group III nitride compound semiconductorand formed on a sapphire substrate.
 17. A group III nitride compoundsemiconductor device according to claim 14, wherein said undercoat layeris made of Al_(X)Ga_(1-X)N (0≦X≦1).
 18. A group III nitride compoundsemiconductor device according to claim 17, wherein said undercoat layeris formed of an AlN layer.
 19. A group III nitride compoundsemiconductor device according to claim 18, wherein said AlN layer has athickness of from 0.2 to 3.0 μm.
 20. A group III nitride compoundsemiconductor device according to claim 18, wherein said AlN layer has athickness of from 0.5 to 1.5 μm.
 21. A group III nitride compoundsemiconductor device according to claim 14, wherein said undercoat layeris formed of a silicon single crystal.
 22. A group III nitride compoundsemiconductor device according to claim 14, further comprising asedimentary layer interposed between said undercoat layer and saidsubstrate.
 23. A group III nitride compound semiconductor deviceaccording to claim 14, wherein said substrate is made of one ofsapphire, silicon single crystal and silicon carbide single crystal. 24.A group III nitride compound semiconductor device according to claim 14,further comprising a reflection layer formed on said surface of saidundercoat layer and made of nitride of at least one kind of metalselected from the group consisting of titanium, zirconium, hafnium andtantalum, said reflection layer having a surface shape formed inaccordance with a surface shape of said undercoat layer.
 25. A group IIInitride compound semiconductor device according to claim 24, whereinsaid reflection layer is made of titanium nitride.
 26. A group IIInitride compound semiconductor device according to claim 24, whereinsaid substrate is made of sapphire, said undercoat layer is made of AlNand having a surface formed as a texture structure, and said reflectionlayer is made of titanium nitride.
 27. A group III nitride compoundsemiconductor device comprising: a substrate; a group III nitridecompound semiconductor layer having a device function; and an undercoatlayer formed between said substrate and said group III nitridesemiconductor layer, said undercoat layer having a surface which is pitshaped.
 28. A group III nitride compound semiconductor device accordingto claim 27, wherein said undercoat layer is formed substantially of asingle crystal.
 29. A group III nitride compound semiconductor deviceaccording to claim 28, wherein said undercoat layer is formed of a groupIII nitride compound semiconductor and formed on a sapphire substrate.30. A group III nitride compound semiconductor device according to claim27, wherein said undercoat layer is made of Al_(X)Ga_(1-X)N (0≦X≦1). 31.A group III nitride compound semiconductor device according to claim 30,wherein said undercoat layer is formed of an AlN layer.
 32. A group IIInitride compound semiconductor device according to claim 31, whereinsaid AlN layer has a thickness of from 0.2 to 3.0 μm.
 33. A group IIInitride compound semiconductor device according to claim 31, whereinsaid AlN layer has a thickness of from 0.5 to 1.5 μm.
 34. A group IIInitride compound semiconductor device according to claim 27, whereinsaid undercoat layer is formed of a silicon single crystal.
 35. A groupIII nitride compound semiconductor device according to claim 27, furthercomprising a sedimentary layer interposed between said undercoat layerand said substrate.
 36. A group III nitride compound semiconductordevice according to claim 27, wherein said substrate is made of sapphireor silicon single crystal.
 37. A group III nitride compoundsemiconductor device according to claim 27, further comprising areflection layer formed on said surface of said undercoat layer and madeof nitride of at least one kind of metal selected from the groupconsisting of titanium, zirconium, hafnium and tantalum, said reflectionlayer having a surface shape formed in accordance with a surface shapeof said undercoat layer.
 38. A group III nitride compound semiconductordevice according to claim 37, wherein said reflection layer is made oftitanium nitride.
 39. A group III nitride compound semiconductor deviceaccording to claim 37, wherein said substrate is made of sapphire, saidundercoat layer is made of AlN and having a surface formed as a texturestructure, and said reflection layer is made of titanium nitride.
 40. Agroup III nitride compound semiconductor device comprising: a substrate;a group III nitride compound semiconductor layer having a devicefunction; and an undercoat layer formed between said substrate and saidgroup III nitride semiconductor layer, said undercoat layer having asurface containing inclined faces, wherein a projected area ratio ofsaid inclined faces to said surface of said undercoat layer on a planeof projection is in a range of from 5 to 100%.
 41. A group III nitridecompound semiconductor device according to claim 40, wherein theprojected area ratio of said inclined faces to said surface of saidundercoat layer on a plane of protection is in a range of from 30 to100%.
 42. A group III nitride compound semiconductor device according toclaim 40, wherein the projected area ratio of said inclined faces tosaid surface of said undercoat layer on a plane of protection is in arange of from 70 to 100%.
 43. A group III nitride compound semiconductordevice according to claim 40, wherein said undercoat layer is formedsubstantially of a single crystal.
 44. A group III nitride compoundsemiconductor device according to claim 43, wherein said undercoat laseris formed of a group III nitride compound semiconductor and formed on asapphire substrate.
 45. A group III nitride compound semiconductordevice according to claim 40, wherein said undercoat layer is made ofAl_(X)Ga_(1-X)N (0≦X≦1).
 46. A group III nitride compound semiconductordevice according to claim 45, wherein said undercoat layer is formed ofan AlN layer.
 47. A group III nitride compound semiconductor deviceaccording to claim 46, wherein said AlN layer has a thickness of from0.2 to 3.0 μm.
 48. A group III nitride compound semiconductor deviceaccording to claim 46, wherein said AlN layer has a thickness of from0.5 to 1.5 μm.
 49. A group III nitride compound semiconductor deviceaccording to claim 40, wherein said undercoat layer is formed of asilicon single crystal.
 50. A group III nitride compound semiconductordevice according to claim 40, further comprising a sedimentary layerinterposed between said undercoat layer and said substrate.
 51. A groupIII nitride compound semiconductor device according to claim 40, whereinsaid substrate is made of one of sapphire, silicon single crystal andsilicon carbide single crystal.
 52. A group III nitride compoundsemiconductor device according to claim 40, further comprising areflection layer formed on said surface of said undercoat layer and madeof nitride of at least one kind of metal selected from the groupconsisting of titanium, zirconium, hafnium and tantalum, said reflectionlayer having a surface shape formed in accordance with a surface shapeof said undercoat layer.
 53. A group III nitride compound semiconductordevice according to claim 52, wherein said reflection layer is made oftitanium nitride.
 54. A group III nitride compound semiconductor deviceaccording to claim 52, wherein said substrate is made of sapphire, saidundercoat layer is made of AlN and having a surface formed as a texturestructure, and said reflection layer is made of titanium nitride.
 55. Agroup III nitride compound semiconductor device comprising: a substrate;a group III nitride compound semiconductor layer having a devicefunction; an undercoat layer formed between said substrate and saidgroup III nitride semiconductor layer; and a sedimentary Layer formedbetween said undercoat layer and substrate, said undercoat layer beingformed of a group III nitride compound semiconductor and having one of asurface of a texture structure, a surface of a sectional trapezoidshape, and a surface of a pit shape, said sedimentary layer being formedof one of a group III nitride compound semiconductor and a metal nitridecompound semiconductor.
 56. A group III nitride compound semiconductordevice according to claim 55, wherein said sedimentary layer is formedas a multilayer containing at least first and second sedimentary layersand another group III nitride compound semiconductor layer is interposedbetween said first and second sedimentary layers.
 57. A group IIInitride compound semiconductor device according to claim 55, whereinsaid sedimentary layer is formed of Al_(X)Ga_(1-X)N (0≦X≦1) and formedat a temperature lower than or equal to that of said undercoat layer.58. A group III nitride compound semiconductor device according to claim55, wherein said sedimentary layer is formed of a metal nitride compoundsemiconductor and formed at a temperature lower than or equal to that ofsaid undercoat layer.
 59. A group III nitride compound semiconductordevice according to claim 55, wherein said undercoat layer is made ofAl_(X)Ga_(1-X)N (0≦X≦1).
 60. A group III nitride compound semiconductordevice according to claim 59, wherein said sedimentary layer is formedof an AlN layer.
 61. A group III nitride compound semiconductor deviceaccording to claim 60, wherein said substrate is formed of sapphire orsilicon single crystal.
 62. A group III nitride compound semiconductordevice according to claim 61, wherein said sedimentary layer is formedon face a of said sapphire substrate.
 63. A grout III nitride compoundsemiconductor device according to claim 55, further comprising: areflection layer formed on said surface of said undercoat laser had madeof nitride of at least one grind of metal selected from the groupconsisting of titanium, zirconium, hafnium and tantalum, said reflectionlayer having a surface shape formed in accordance with the surface shapeof said undercoat layer.
 64. A group III nitride compound semiconductordevice according to claim 63, wherein said reflection layer is made oftitanium nitride.
 65. A group III nitride compound semiconductor deviceaccording to claim 63, wherein said substrate is made of sapphire, saidundercoat layer is made of AlN and having a surface formed as a texturestructure, and said reflection layer is made of titanium nitride.